1. Field of the Invention
Such fuses serve the purpose of protecting circuit parts against thermal overload, particularly due to surge voltages, and can be utilized in arbitrary circuits, for example on printed circuit boards. A preferred employment of the inventive thermal fuse, is film circuits, particularly thick-film hybrid circuits as employed, for example, in telecommunications.
2. Description of the Prior Art
A thermal fuse of the species initially cited is disclosed, for example, by DE 42 19 554 A1. The fuse disclosed therein is a matter of a bow fuse that is secured at two solder points. The thermal fuse is electrically connected in series with a defined thick-film resistor in the ceramic substrate. When voltage is applied, the current that flows through heats the ceramic via the resistance layer, said ceramic thermally stressing at least one of the two solder locations of the fuse due to aptly selected hot spots and softening it given a current overload. The known bow fuse must first be pre-stressed after being soldered on, so that a spring clipxe2x80x94given overloadxe2x80x94snaps away from the softened solder location and thus interrupts the electrical connection.
A bow fuse that was activated cannot be reset into the initial conditions and, replaced without further ado. What is also problematical given the known fuse type is that the softening process of the solder andxe2x80x94accompanying this the release of the spring clip and, the interruption of the current is a relatively slow and not very abrupt process.
The invention is therefore based on the object of creating a thermal fuse of the species initially cited that, on the one hand, can be utilized relatively universally in various circuits but that, on the other hand, can in turn be reset with optimally little outlay after an activation and that, moreover, should exhibit a fast and abrupt trigger behavior that assures a correct interruption of the current in case of malfunction.
In a thermal fuse of the species initially cited, this object is inventively achieved in that
a planar thermal bimetal snap element is provided
that is secured on the circuit substrate by at least one solder location with refractory solder and that is thermally coupled to the substrate,
wherein the solder location is fashioned as first contact location for connection to a corresponding circuit contact of the circuit substrate;
and in that the snap element is mechanically pre-arched hump-like that, given a non-activated fuse, it electrically and conductively contacts a second contact location of the circuit substrate but does not when the fuse is triggered and, thus, the arch of the hump is reversed.